decide or decides ?

[XINLAI-UE]

"What if one of the bulls decide to drop in?"

Do you think this sentence is okay in grammar? But, in my opinion, I think the right one would be: "What if one of the bulls decides to drop in?"
Because L said "one of the bulls", not "bulls", we should use "decides" instead of "decide". This is my opinion, how do you think?
Thanks for your help.



Context:
M: I found our access to the infirmary building, but I'm gonna need some time to make it work.
L: How much time?
M: Enough for me to find my way up a 20-foot vertical drainpipe without using a ladder. I'll probably need to skip P.I. tomorrow if I wanna get this thing done.
L: You can't just skip it. It ain't class. What if one of the bulls decide to drop in?
M: Well, I don't have a choice, do I? ...

[David L.]

Grammatically, yes.
But what nationality is L? They are saying 'gunna' 'wanna' and 'ain't', so don't expect good grammar from them!
Put 'man' at the end of the sentence and I can hear Ali G talking.